Biometric identification systems use sensor technologies to obtain information regarding an individual's unique physical characteristics and compare the obtained information with verified reference information to confirm the identity of the individual. Known biometric identification systems have used optical, thermal, capacitive, impedance, radio-frequency, conductance and ultrasonic based sensors for detecting biometric information.
Physical characteristics that are commonly used for biometric identification include unique features from an individual's facial features or geometry, iris, hand geometry, vein pattern, voice, palm and fingerpads. The most predominantly used physical characteristics for biometric identification are the minutiae or macrofeatures found on the dermal surface of an individual's fingerpad. For example, an individual's fingerpad is covered with a pattern of ridges and valleys commonly referred to as a fingerprint. A typical fingerprint scan contains about 30 to 40 minutiae and macrofeatures which are unique biometric identification characteristics. The dermal surface of an individual's finger also has between 50 and 300 sweat gland pores located on the fingerprint ridges. Like an individual's fingerprint, the number and locations of sweat gland pores on an individual's fingerpad do not change and provide unique biometric identification characteristics. Moreover, the locations of an individual's sweat gland pores relative to the fingerprint minutiae or macrofeatures provides an additional biometric identification measure.
The common traits to biometric identification measures are their permanence and uniqueness. However, these basic traits also make the biometric identification systems vulnerable to spoofing. Spoofing is the act of using an artificial biometric sample (such as a “fake finger”) containing a replica of an authorized individual's fingerpad to enable an unauthorized individual to gain access to a secured system. Spoofing may also be used to enable an individual to pass himself off as another individual at a security checkpoint. Typically, the replicated fingerpad is formed of a synthetic material such as gelatin (including gummi which is obtained by gelling aqueous solution of gelatin), silicone, epoxy, latex and the like.
Anti-spoofing systems typically are designed to detect the liveness of the physical sample presented to the biometric detection sensor. Most of these systems involve relatively large sensors which are unacceptable for mobile or portable devices. In addition, anti-spoofing systems are typically directed to detecting a liveness measure of the finger such as finger surface resistance, temperature, pulse, moisture, and blood oximetry. These systems, however, can be circumvented because they operate by comparing the detected liveness measure value to a predetermined acceptable range. Namely, it is possible to design an artificial biometric sample which produces a detected liveness measure within a known acceptable range. For example, artificial biometric samples can be made of materials with electrical properties resembling that of a living finger and which yield a biometric liveness measure within a given acceptable range.